Expanding piston



March 3, 1931 c. p. STROMGREN EXPANDING PISTON 2 Sheets-Sheet 1 "Filed Jan.

- Mfg/r012 U la/94553512019625 y l? fimd/ @TTOENE Y MarchB, 1931. c. D. STROMGREN EXPANDING" PISTON Filed Jan. 2, 1930 a Sheets-Sheet 2 Patented Mar. 3, 1931 n 'TAS PATENT OFFHCE CHARLES D. STROMGREN, OF LOS ANGELES, CALIFORNIA EXPANDING PISTON This invention has to do with pistons. and is more partlcularly related to pistons for internal combustion engines, which, due to the wide range of temperature under which they operate and high temperature attained during operation, are usually a sourceof considerable trouble in the design and operation of such engines. a

It is, of course, well known to thosefamiliar with the construction and operation of internal combustion engines, that a certain amount of a clearance is required between the piston and the cylinder wall. This clearance not only allows movement of the pistons in the cylinders, but also permits lubricating oil films to accumulate between the otherwise contacting metal surfaces. The clearance must be suflicient to permit the movement of the piston in the cylinders throughout the en- 2 tire range of temperatures to which the piston is subjected in the operation of the motor. In other words, the clearance must be sufficient to permit expansion of the piston due to its rise in'temperature without seizure or sticking within the cylinder. The clearance must also be suiiicient to permit a certain amount of distortion in the piston due to the pressure to which it is subjected.

It has become a common practice, in recent motor design, to reduce the weight of the piston by making the same of aluminum or some light alloy metal. Due to the great difference in the coefficients of expansion, be-

' tween metals of this character and the metal used in theengine blocks it is necessary to allow more clearance between the pistons and the cylinders when the pistons are made of metals of the character referred to, than is .the case when they are made of the same metal as the engine block. This means, that in order to have sufiicient clearance, when the piston is at its highest temperature, it must have an excessive clearance when it is at its lowest temperature.

Excessive clearance permits the escape of gas under pressure to the crank case and oil reservoir thus. destroying the lubricating properties of the oil and also allows an excess quantity of lubricating oil to be drawn into the combustion space during the suction stroke. Excessive'clearance, is therefore the principal source of mostengine difliculties and is conducive to noises caused by the clattering and slapping action of the piston which produces rapid wear in both the piston and the cylinder.

From the above it will be seen that an ideal pistonv for an internal combustion engine, is one which will fit with constant clearance, under all operating conditions. In other words, the ideal piston will have correct mechanical clearance at low temperatures and will, at the same time, not bind or seize from thermal expansion when it reaches its maximum temperature. To approach this ideal, certain manufacturers slit or slot the piston in a manner which is intended to insure the partial collapse of the piston during the expansion of the metal at elevated temperatures. Pistons of this character have been found to be more or less satisfactory until they have. been reduced in size by wear to a point at which they no longerproperly cooperate with the cylinder wall. The-aluminum alloy metals, being softer than the material of which the cylinders are made, wear very rapidly and replacement of the pistons soon becomes necessary since no provision has been made for compensating for such wear.

The primary object of this invention is to produce a piston of the class described, embodying means for holding the piston properly to the cylinder bore with constant clearance therein under all operating conditions.

The piston contemplated by this invention, when operated in a cylinder as intended, has compensating means adapted to permit the expansion or contraction of the metal of the piston without changing the geometric dimcnsion across the opposed bearing areas of the shirt. The piston, therefore, operates without dragging and binding because of tightness and without knocking and wearing rapidly because of looscness. The piston also embodies adjusting meansfor regulating the con'ipensating means referred to above as well as for changing the distance between the opposed bearing surfaces.

One advantageous feature of the piston contemplated by this invention, is that the adjustment referred to above, may be efiected without removing the piston from the cylinder. This adjustment, in one form of my invention, is made from below the piston and can be carried out at any time on removal of the crank case. It will be seen that this adjustment may be made incidental to an inspection and tightening of the connecting rod bearings. In another form of my invention this adjustment may be effected from above the piston at any time on removal of the cylinder head and may be made incident to the grinding of the valves.

The general construction of the piston, contemplated by this invention, is substantially the same as any ordinary internal combustion engine piston. The piston embodies a head or drum member and a skirt, provided with ring grooves and wrist pin bearings. The skirt of the piston is in the preferred form of my invention, provided with two slots or slits, located near the top and bottom of the piston on one or both sides of the wrist pin bearings. These slots are substantially parallel with the head of the piston and are connected preferably at their mid points with a third forming an H in the skirt of the piston and consequently producing two sections, which will be hereinafter referred to as cooperating to form a flexible skirtv section. In order that the outward flexing movement of these two sections, formed by the three slots, referred to above, may be assured I prefer to cast the skirt with creases or hinge members which are positioned at the point at which each of the sections joins the main part of the piston skirt. Means for imparting adj ustable expansion to the flexible section, as mentioned above are provided within the piston and it is to be understood that while I prefer to provide the skirt with a flexible section or sections formed by the H slot referred to above, the adjusting means are applicable to any slotted piston and may be employed in connection with slots which run the full length ofthe skirt. The hinge portions or creases referred to above may also be used in connection with slots which run the full length of the skirt, and in pistons embodying this feature, the skirt of the piston is not distorted and the pin bearings are therefore not disalined as would be the case in a continuous skirt.

The details in the construction of certain" my invention and shows a preferred form of adjustment for effecting the expansion of the flexible skirt section,

Fig. 3 is a sectional elevation which may be considered as having been taken in a plane represented by the line 3-3 of Fig. 2,

Fig. 4, is an inverted plan section, which may be considered as having been taken in the plane represented bythe line 44 in Fig. 3,

Fig. 5, is a sectional elevation similar to Fig. 3, but showing another form of adjusting means which is accessible through the upper portion of the cylinder,

Fig. 6, is a plan section which may be considered as having been taken in a plane represented by the line 66 in Fig. 5, and

Fig. 7, isa plan section, similar to Fig. 6, but illustrating another form of adjustable expanding member used in imparting adj ustment to an adjustable skirt section.

More particularly describing the invention as herein illustrated, reference numeral 11 indicates a piston which is of the same general construction commonly used in internal combustion engines in that it embodies a head or drum 12, and a skirt 13, which is provided with ring grooves 14 and wrist pin bearings 15, The skirt 13 has formed therein, a flexible section or a pair of'fiexible sections, indicated at 16, situated on one or both sides of the wrist pin. The flexible section 16, is formed by cutting two substantially parallel slots in the skirt of the piston which are situated as indicated by reference numerak 17 and 18; the slot 17 being located below the bottomring groove-and the slot 18 being located slightly above the bottom of the piston skirt so as to form a rigid section or ring 19 below the flexible section 16. The slots 17 and 18 are connected by a third slot 20 which preferably connects the slots 17 and 18 at their mid points forming an H and as mentioned above, the piston is preferably cast with creases or inwardly projecting folds 21 which are situated at the outer edges of the two curved plates 16a and 166 which cooperate to form the flexible section 16. These creases or hinge sections 21, which are best illustrated in the section shown in Fig. 4, are designed to impart an outwardly flexing stress in the sidewall sections 16a and 16b.

The ring portion 19 of the'skirt is designed to impart rigidity to the piston and since this portion is situated a substantial distance below the head 12, which is exposed to the high temperature of the combustion chamber, it has been my observation that the high temperatures from the head 12 are conducted to the walls of the cylinder so'that the bottom portion 19, of the piston, is not: subjected to the wide rangeof temperature variation encounterml in the mid section of the piston. For this reasonl prefer not to extend the vertical slot 20 to the bottom of the skirt. but

have made the same through that section of the piston which is subjected to the wide range of temperatures mentioned above.

Figs. 2 to 4 inclusive, illustrate in detail the tion of the vertical slot or slit 20. The hub 23 is internally threaded for the reception of a hollow pin 24c, which is provided with a head 25 by means of which it may be adjusted within the hub. The hollow portion 26 of the pin 24: receives a coil spring 27 which engages a plunger 28, having a head 29 removably mounted on its outer end and adapted to rest against the inner surface of the mid portions of'skirt sections 16a and 16b. This construction permits the application of outward pressure to the flexible section 16 by" ad vancing the pin 21 in the hub. It will be seen that the flexible section 16 is held outward in a yieldable manner, by the plunger 28, which engages the coil spring 26 so that the section 16 may be pressed inwardly by engagement with the cylinderwalls at high temperatures and will be flexed outwardly by the action of the coil spring 27 at low temperatures. This yieldable adiustment, therefore, not only permits the correction of the diameter of the piston 11, but it holds theflexible section 16 in sliding engagement with the cylinder wall at all temperatures.

It was mentioned above that the piston skirt may be provided with one or two flexible sections and in Fig. 3 I have shown in dot and dash lines indicated at A the manner in which this form of piston may be provided with a pair of oppositely disposed flexible sections and adjusting means.

Figs. 5 and 6, illustrates a modification in the construction of the adjusting means whereby the flexible'sections 26 and 26 may be adjusted from above the piston head 12a. Figs. 5 and 6 show the piston as being provided with two flexible sections, but it is to be understood that the same general construction shown in Figs. 2 to .4 inclusive may be followed in the construction of the pistions shown in Figs. 5 and 6. The skirt sections 26a and 26b and 26a and 26.1) are shown as having provided at their mid portions, adjacent the vertical slits 27 and 27, pairs of parallel downwardly tapered lugs or pr0jections 28 and 28. The central portion of the head 12; is shown as being provided with a downwardly extending boss 29 which is situated below a recess 30 and is threaded to receive a screw pin 31. The screw pin 31 extends downwardly below the boss and has provided at its lower end a head 32 which supports a. flat spring member 33 and arm angularly bent leaf spring 33. The spring 33' has two downwardly extending fingers 84c and 34", the lower ends of which are in sliding engagement with the bosses 28 and 28, and the upward movement of the screw 31 acting on the member 33 throws the fingers 34: and 34 upwardly, and thereby holds the flexible sections 26 and 26 outward in a yieldable manner against the tension of the spring .members 33 and 33'. A locknut 35 is pro-- vided in the recess 30 for the purpose of locking the screw 31 many predetermined position.

Fig. 7 shows a modified form of expandin means for imparting adjust-able expansion to the flexible section 41 composed of skirt sections 41a and 416. In this form of expander, the inner surfaces of each of the sections 1141 and 115 are provided with bosses or lugs 42a and 42b respectively. Each of these lugs is provided with a recess or a passage indicated at 43a and 43?) respectively. Adjustable means, for expanding the two sections 11a and 41?), are shown as comprising an expanding unit indicated generally by reference numeral 44. This unit embodies a bolt or screw member 45 provided with head 46 adapted to rest in the recess 43a in the boss 42a. The end of the bolt opposite the head- 16 is slidably received withina sleeve 4'2,

formed on the inner end of a head member 18 which restsin the recess or passage 43b in the boss 42?). The head member 48, is provided with a shoulder 49 which is engaged by a coil spring 50, the tension of the coil spring 50 is regulated by means of a sleeve-nut '51- which is in threaded engagement with the bolt 45. It will be seen that as the nut 51 is moved toward the shoulder 49 that the two bosses 42a and 42b and their associated parts, the skirt sections 410. and 41?), are yieldably pressed away from each other. The sleeve nut 51 may be locked in any predetermined position by means of the locknut 52.

' From the foregoing description, it will be seen that my invention, in all of its forms. comprises a piston, embodying a flexible skirt a section which is associated with means for is substantially the same as that of the engine block, this adjustment may be made of a rigid nature and the'overall cost of such a piston thereby reduced through the elimination of the various types of springs.

It is to be understood therefore that, while I have herein described and illustrated one preferred from and certain modifications in my invention, the invention is not limited to means comprising an arm mounted in the top of said piston and having a downwardly extending portion terminating-in a hub opposite said flexible section, and screw means in said hub for applying pressure to said flexible section. v

2. A piston embodying: ahead; a skirt; a flexible section in said skirt, said. flexible section being formed by two slots in said shirt in planes substantially parallel with said head and a third slot connecting the two first mentioned slots; and means for adjustably expanding said flexible section, said expanding means comprising an arm mounted. in the top of said piston and having a downwardly extending portion terminating in a hub opposite said flexible section, and screw means in said hub for yieldably applying pressure to said flexible section.

3. A piston embodying: a head; a skirt; a

flexible section in said skirt and means for expanding said flexible section, said expanding' means comprising an arm mounted with in said piston and having an extending portion terminating in a hub opposite said flexible section and threaded means in said hub for applying pressure to said section. a. A piston embodying: a head; a skirt; a flexible section in said skirt and means for expanding said flexible section, said expanding means comprising an arm mounted within said piston and having an extending portion terminating in a hub opposite said flexible section, a hollow screw in said hub, a spring in said screw, and a plunger in said screw engaging said spring for applying pressure to said flexible sections,

5, A piston embodying: a head; a skirt; a flexible section in said skirt, said flexible section being formed by two slots in said skirt in planes substantially parallel with said head and a third slot connecting the two first mentioned slots; and means for adjustably expanding said flexible section, said expanding means comprising an arm mounted in the top of said piston and having a downwardly extending portion terminating in a hub opposite said flexible section; and yieldable means associated with said hub for applying pressure to said flexible section.

6. A piston embodying: a head; a skirt; a flexible section in said. skirt and means for expanding said flexible section, said expandtion terminating in a hub opposite said fiexi- H ble section; and yieldable means in said hub for applying pressure to said section.-

7. A piston embodying: a head; a skirt; a

flexible section in said skirt; and means for expanding said flexible section, said expanding means comprising an arm mounted within said piston terminating opposite said flexible section; and yieldable means associated with said arm for applying pressure to said flexible section.

In testimony whereof, I have hereunto set my hand at Los Angeles, California, this 26th day of December, 1929.,

CHARLES D. STROMGREN. 

